The use of lanthanide-containing polymerization catalysts that include aluminoxane are known in the production of desirable polymers having high levels of live ends and cis content. However, the activity of the catalyst system is very high, thus making use of the catalyst difficult on a commercial scale. For example, as the activity of the catalyst becomes more aggressive, the time required to achieve a given conversion level is reduced, and consequently, it becomes more difficult to remove the heat of polymerization at a sufficient rate. Accordingly, there is a need for a process that will allow use of active catalyst systems that produce high polymerization rates which could not normally be tolerated in conventional processes.